1. Field of the Invention
The invention relates to a method of manufacturing ceramics, particularly suspension insulators and other similar ceramics having a small diameter hollow cylindrical central core portion with a closed head portion and a large diameter shed portion extending from the central core portion in a radial direction.
2. Description of the Related Art
Hitherto, such a suspension insulator and the like having a small diameter hollow cylindrical central core portion and a large diameter shed portion has been manufactured by use of a porous mold. The porous mold comprises a porous mold body including a central portion and a peripheral portion and having a mold surface of a shape corresponding to an outer shape of ceramics to be molded, that is, outer shapes of the central core portion and the shed portion of the suspension insulator, and a porous tube embedded in the porous mold body along the mold surface.
In a conventional method of manufacturing the suspension insulator or the like, a batch is pressed on the mold surface, and closely adhered to the mold surface by applying a negative pressure to the whole mold surface through the porous tube to mold a molded product in a precise shape. After molding, pressurized air is blown out of the mold surface to release the molded product from the mold surface to thereby remove the molded product from the porous mold.
However, in the aforementioned conventional method, there are problems of mold cracks generated by a molding load owing to lowering of strength of the porous mold having a high porosity, deformation of the molded product caused by an excess air blow pressure acting on the molded product at the time of releasing the molded product from the porous mold, impossible releasability by a poor air blow pressure, breakage of the molded product at the boundary portion between a small diameter central core portion and a large diameter shed portion, deformation by rising of the head portion of the molded product and the like.